Scientists at the Australian National University are investigating the use of crystals of the mineral zircon as a thermometer of the past to reconstruct the conditions of the primeval Earth. Ancient zircon crystals are environmental archives, trapping atoms of elements that give hints on the landscape in which they formed.

The concentration in zircons of one such element, titanium, has been used to gauge the temperature of past landscapes. During crystallisation, titanium atoms in the magma melt in which zircon forms replace some of the silicon atoms in the mineral’s zirconium silicate crystal lattice. The higher the temperature of crystallisation the more titanium gets locked up.

Nick Tailby, of the Research School of Earth Sciences, is synthesising zircons to see if the chemical composition of the magma also affects the amount of titanium incorporated. Earlier ANU research, led by Mark Harrison, centred on zircons from the Jack Hills deposit near Meekatharra in Western Australia. At 4.4-billion years old, the purple zircons crystallised soon after the Earth started to form 4.56 billion years ago. Harrison’s team found that they formed in magma at 700 degrees C, cool by geological standards. The scientists concluded that they must have formed in water near the surface of the Earth. It was evidence for oceans as early as 4.4 billion years ago.

Now Tailby, a final year PhD student supervised by John Mavrogenes, is fine tuning the titanium thermometer to see how the amount of silica in the magma melt affects the concentration of titanium in the zircon crystals. He is using a high pressure furnace to crystallise zircons from synthetic magma of varying silica concentrations. He probes the zircons at the Advanced Photon Source, a synchrotron facility at Argonne National Laboratory in Chicago, and is set to conduct further research at the Australian Synchrotron in Melbourne. (Synchrotron radiation is high intensity x-rays.)

Tailby, from Melbourne, did his Bachelor of Science degree at ANU. He caught the geology bug when he worked at RSES on a Summer Research Scholarship. “It’s a really good way of trying before you buy,” he says. “Being in that research environment was nice.” He spent half of his Honours year in South Africa on a scholarship sponsored by the Australian Institute of Mining and Metallurgy, and plans to stay in academia, doing post-doctoral research overseas, perhaps in the United States.